Emptying fresh water from onboard tank

Hi, I'm struggling to understand quite how things work on site with regard to fresh water in my motorhome?  I've sorted the grey waste with a Wastemaster in case I'm unable to empty over a grid on site, but now I need to ask about the fresh water.  I didn't fill / use the motorhome onboard water tank when away for the first time last week, because I wasn't sure where to empty what I hadn't used before driving home. (No grid on site)  Please can someone help with this?  Also, I assume a long hose pipe is necessary for filling the tank, and if so, what sort of connections are generally needed please? Many thanks.